Refrigeration systems have been in existence since the early 1900s, when reliable sealed refrigeration systems were developed. Since that time, improvements in refrigeration technology have proven their utility in both residential and industrial settings. In particular, very low temperature refrigeration systems currently provide essential industrial functions in biomedical applications, cryoelectronics, optical coating operations, industrial and commercial coating operations, and semiconductor manufacturing applications. Refrigeration systems manufacturers are also faced with increasingly restrictive environmental regulations that have driven the refrigeration industry away from chlorinated fluorocarbons (CFCs) to hydrochlorinated fluorocarbons (HCFCs), and more recently, to hydrofluorocarbons (HFCs) due to a European Union law (in effect January 2001) banning use of HCFCs.
System floor space is yet another consideration for the refrigeration industry. The semiconductor industry, for example, is very concerned about reducing the overall system footprint. As a result, refrigeration systems manufacturers continue to develop refrigeration systems that use compact components without sacrificing performance and capacity.
Where horizontal floor space is more limited than vertical space, it is beneficial to use the available vertical space if possible. As an example, reciprocating and screw compressors are typically designed horizontally. Semi-hermetic reciprocating compressors are particularly large, adding to the required floor space of a refrigeration system. By contrast, efficient, high capacity scroll compressors are designed vertically, thereby taking advantage of available vertical space and reducing the size of the overall system footprint.
Other fields of application are in the biological storage, and pharmaceutical and chemical processing. Very low temperature mixed refrigerant systems have been used in biological freezers and can be used in processing of pharmaceutical products and chemicals for the purpose of controlling process reactions or to otherwise control these processes. Other applications include freeze-drying of pharmaceutical and biological agents, reagents and other substances, and freeze drying of food products.
The concept of a scroll compressor is about 100 years old. However, only in the last 20-30 years have the required machining tolerances been achievable to make this design achievable on a commercial scale. Beginning in the late 1980's and early 1990's scroll compressors began to be commercialized, mainly for residential and commercial air conditioning applications. By the mid 1990's refrigeration scrolls began to be used for commercial refrigeration applications (i.e. supermarket refrigeration).
These modern scroll compressors feature a vertical design in which the motor shaft is vertical, and the motor is in the lower part of the compressor housing and extends down to the compressor oil sump. The scrolls sit above the motor. The orbiting scroll is moved by the motor shaft, while the stationary scroll is held in place above the orbiting scroll.
The typical reciprocating compressor discharge temperature in very low temperature refrigeration systems is in the range of 110 to 130° C. 130° C. is typically a maximum allowable discharge temperature (as measured at the compressor service valve). Steady state operation will typically be limited temperatures lower than 130° C. Temperatures in excess of 130° C. result in decomposition of the compressor oil and subsequent metal wear which results in a compressor failure.
Scroll compressors tend to have higher compressor discharge temperatures. To remain competitive with alternate compressors liquid injection was developed for the refrigeration scrolls to manage compressor discharge temperature and improve refrigeration capacity.
In a typical unit, the discharge temperature of a scroll compressor imposes a significant limitation on the operating conditions of the compressor and reduces overall system efficiency. Some influencing factors are the composition of the overall mixture, and the compressor discharge and suction pressures. Therefore, it is desirable to find a means to lower the discharge temperature for a given refrigerant system to enable operation at a lower evaporator temperature or with greater refrigeration capacity at a given evaporator temperature.
Stated another way, it is desirable to maintain the discharge temperature in a safe range while optimizing the overall system performance to achieve greater overall efficiency. For purposes of reference, efficiency can be compared against Carnot efficiency. See for example “Performance of Throttle-Cycle Coolers Operating With Mixed Refrigerants Designed for Industrial Applications in a Temperature Range 110 to 190 K”, by Podtcherniaev, Boiarski and Flynn, published in Advances in Cryogenic Engineering: Proceedings of the Cryogenic Engineering Conference, Vol 47 (2002).
One known method of cooling the compressed gas is to inject liquid refrigerant from the condenser through an injection passage directly into the compressor. The liquid refrigerant may be injected into the suction gas area of the compressor or it may be injected into the intermediate enclosed space defined by the scroll members (see for example U.S. Pat. No. 5,640,854 and U.S. Pat. No. 5,076,067).
The evolution of refrigerant use has changed the design and function of refrigeration systems. Traditionally, an alkylbenzene compressor oil, or mineral oil, was used with CFC and HCFC systems. However, HFCs are much less miscible and are considered to be immiscible in alkylbenzene oil, so a polyolester (POE) compressor oil is typically used to be miscible with the HFC refrigerants. Refrigeration systems manufacturers must comply with the current environmental laws dictating refrigerant selection and must also provide ways to cope with the impact that the refrigerant component selection has on refrigerant related components, such as compressors, and the compressor oil.
Currently major manufacturers of the scroll compressors such as Copeland, and others, have selected, tested and approved POE oils, which are compatible with conventional refrigerants such as R134a, R404A, and R507. These oils demonstrate good miscibility properties with these refrigerants at temperatures above −45° C. (−49° F.). Oil ejected from the compressor into the discharge line returns back to the compressor carried by the refrigerant, so commercial refrigeration systems don't require oil separators.
What is needed is a refrigeration system with a compressor that is compatible with certain POE oils, which are miscible with refrigerants below −45° C. (−49° F.).
Several attempts have been made to develop an efficient, compact refrigeration system that is compatible with modern refrigerants.
U.S. Pat. No. 6,098,421, Fujita, et al., Aug. 8, 2000, entitled “Refrigerating apparatus,” discloses a liquid injection type scroll compressor used in a refrigerating apparatus using hydrofluorocarbon refrigerant which does not contain chlorine (HFC-125/HFC-143a/HFC-134a) as an operating fluid and an amount of an injected liquid is controlled according to a discharge temperature of the compressor. Further, ester oil and/or ether oil is used as refrigerator oil and a dryer is disposed in a refrigerating cycle. With this arrangement, a refrigerating cycle operation can be stably realized in a wide range without always changing the arrangement of a conventional refrigerating apparatus.
U.S. Pat. No. 6,073,454, Spauschus et al., Jun. 13, 2000, entitled “Reduced pressure carbon dioxide-based refrigeration system,” discloses a novel refrigeration apparatus and a method of refrigeration. The novel refrigeration apparatus comprises a desorber/evaporator, a scroll compressor operatively connected to said desorber/evaporator, a resorber/condenser operatively connected to said compressor, an expansion device operatively connected to said resorber/condenser and to said desorber/evaporator and a circulating refrigerant comprising carbon dioxide and a liquid co-fluid in which the carbon dioxide is differentially soluble. The refrigeration method comprises compressing carbon dioxide gas and a liquid co-fluid in a scroll compressor to an increased pressure, such that carbon dioxide at least partially dissolves in the liquid co-fluid, and reducing the pressure on the liquid co-fluid containing the dissolved carbon dioxide so that dissolved carbon dioxide comes out of solution with the liquid co-fluid, and recirculating the gaseous carbon dioxide and liquid co-fluid to the scroll compressor.
U.S. Pat. No. 6,055,827, Tojo, et al., May 2, 2000, entitled “Refrigerant compressor and refrigerating apparatus,” discloses a refrigerating apparatus with a scroll compressor having a compressing section sucking and compressing a hydrofluorocarbon-based refrigerant, a condenser and the like, in which a plain bearing slidably supporting a driving shaft driving the compressing section of the scroll compressor is made of a material containing lead, and an ether oil miscible with the refrigerant used in a refrigerant circuit is used as a lubricant for lubricating the plain bearing.
U.S. Pat. No. 6,006,542, Tojo et al., Dec. 28, 1999, entitled “Refrigerant compressor and refrigerating apparatus,” discloses a refrigerating apparatus with a scroll compressor having a compressing section sucking and compressing a hydrofluorocarbon-based refrigerant, a condenser and the like, in which a plain bearing slidably supporting a driving shaft driving the compressing section of the scroll compressor is made of a material containing lead, and an ether oil miscible with the refrigerant used in a refrigerant circuit is used as a lubricant for lubricating the plain bearing.
U.S. Pat. No. 5,910,161, Fujita, et al., Jun. 8, 1999, entitled “Refrigerating apparatus,” discloses a liquid injection type scroll compressor that is used in a refrigerating apparatus using hydrofluorocarbon refrigerant which does not contain chlorine (HFC-125/HFC-143a/HFC-134a) as an operating fluid and an amount of an injected liquid is controlled according to a discharge temperature of the compressor. Further, ester oil and/or ether oil is used as refrigerator oil and a dryer is disposed in a refrigerating cycle. With this arrangement, a refrigerating cycle operation can be stably realized in a wide range without almost changing the arrangement of a conventional refrigerating apparatus.
U.S. Pat. No. 5,685,163, Fujita et al., Nov. 11, 1997, entitled “Refrigerating apparatus,” discloses a liquid injection type scroll compressor that is used in a refrigerating apparatus using hydrofluorocarbon refrigerant which does not contain chlorine (HFC-125/HFC-143a/HFC-134a) as an operating fluid and an amount of an injected liquid is controlled according to a discharge temperature of the compressor. Further, ester oil is used as refrigerator oil and a dryer is disposed in a refrigerating cycle. With this arrangement, a refrigerating cycle operation can be stably realized in a wide range without almost changing the arrangement of a conventional refrigerating apparatus.
Telemark Cryogenics (Northampton, UK) manufactures a very low temperature refrigeration system that uses a refrigeration scroll compressor. Some of these systems use scrolls equipped for use with liquid injection, but this feature is not used. Unfortunately, this system does not have a desirably high efficiency.
An additional reference describing a scroll compressor in an auto-cascade refrigeration system is an article in the October 1996 issue of American Laboratory, entitled “A mechanically refrigerated cryogenic freezer for air-phase storage of biologicals at −150° C. without liquid nitrogen,” by Robert D. Lehman. This article refers to an air conditioning scroll compressor without liquid injection. Unfortunately, this system does not have a desirably high efficiency.
It is an object of this invention to provide a very low temperature or cryogenic refrigeration system with improved efficiency and decreased size, which complies with current environmental laws dictating refrigerant selection.
It is a further object of this invention to provide a highly efficient, high capacity, compact compressor that allows a reduced refrigeration system footprint.
It is a further object of this invention to provide a refrigeration system with a scroll compressor that manages the refrigerant discharge temperature.